1. Field of the Art
The present invention relates to tachometers, and more particularly, to high performance automotive tachometers.
2. Discussion of the Related Art
In the world of high-speed autoracing, extreme demands are placed on both car and driver. Nowhere is this more true than in the realm of high-speed, short-duration racing, such as drag racing. In these races, drivers command high performance vehicles to accelerate through one-quarter mile of roadway in approximately seven seconds, reaching speeds of over 200 miles per hour. Frequently, the drivers and vehicles are so competitively matched that as little as one thousandth of one second can make the difference between winning and losing a race. Accordingly, drivers look for any way to improve their performance and consistency, even if only by the smallest of margins.
In this regard, drivers train heavily on effective gear shifting. During a typical, seven second racing interval, the driver must normally shift through four or five gears. Indeed, in the professional drag racing circuit driving skill plays a significant role in the outcome of the race. Not only should the driver be able to shift quickly and cleanly, but the driver should also shift at the appropriate engine speeds to extract the maximum power and racing speed from the vehicle. To be sure, the characteristics of any given vehicle (e.g., engine tune, transmission gearing, tires, body aerodynamics, etc.) combine to define a maximum performance curve for each gear of that vehicle. This performance curve, in turn, defines the optium engine speed for each gear at which the driver should shift in order to effect maximum speed from the vehicle. In addition to rote practice, however, drivers also look to instrumentation or other driving aids to help them properly time and execute these critical shifts at the appropriate points along the power curves.
Of course, tachometers have long been known to provide a vehicle operator with an instantaneous display of engine speed. In the area of high performance vehicles, however, tachometers offer special features to provide the extra assistance demanded by the drivers. As an example, some tachometers have a multiple range dial display that expands the critical portion of the dial display. For example, on a circular gauge having a display preprinted near the circumference of the dial face, different scale gradients are provided for different engine speed ranges. Since the lower engine speeds are of lessor significance to the driver for shifting purposes, the scale displaying these lower engine speeds, for example up to 6,000 RPM, is compressed into a small portion of the dial scale display, while the scale displaying higher engine speeds, from 6,000 RPM to 11,000 RPM for example, is expanded to cover the remainder of the dial scale display. In this fashion, the driver can more particularly identify the engine speed in the range surrounding the critical shift points. This type of tachometer can be referred to as a "double range" tachometer.
One known tachometer in the prior art to offer this double range scale utilizes a stepper motor to drive the tachometer pointer or deflection needle. The particular advantage realized by the use of stepper motors is that it is technically easier in a digital circuit to control the deflection needle throughout both the compressed and expanded regions of the dial scale display.
A shortcoming in a stepper motor system, however, resides in the inherent characteristics and limitations of the stepper motor. Since stepper motors are rotated in discrete increments, movement of the tachometer deflection needle is jerky, rather than in smooth, fluid motion. More significantly, the response time of stepper motors is typically too slow for fast revving engines, such as dragster engines. As a result, the engine speed displayed by the tachometer deflection needle lags the actual engine speed. The amount of this "lag" depends upon the rate that the engine speed is changing. This is particularly problematic when the driver targets a specific engine speed at which to shift, since the actual engine speed will be slightly different than the displayed speed.
Other double range tachometers may have the deflection needle controlled by D'arsonval meters. Like stepper motors, however, D'arsonval meters are also characterized by a poor response time that is typically too slow for effective use on dragsters. Furthermore, D'arsonval motors typically have poor vibration resistance, which makes them ill-suited for use on dragsters.
Other engine speed sensing devices are known to provide what can be globally referred to as "RPM switches." These RPM switches are typically individual, stand-alone units adapted to monitor the engine speed and signal or otherwise act upon the detection of certain desired engine speeds. RPM switches are used in a variety of applications such as controlling nitrous oxide injectors, limiting the engine RPM, controlling system ignition timing, and operating shift lights, just to name a few. In a particular vehicle, one RPM switch may be dedicated to control a nitrous oxide injector in such a fashion that the nitrous oxide is controllably injected when the vehicle reaches a preprogrammed engine speed. Similarly, a second RPM switch may be dedicated to controllably advance and retard the ignition timing depending upon the engine speed. A further RPM switch may be dedicated to control a shift light, which illuminates at certain preprogrammed engine speeds to prompt the driver to shift gears. Indeed, shift lights are known to be provided in connection with a RPM switch imbedded within the tachometer.
However, there are various shortcomings in connection with these prior art systems. One shortcoming is the elevated system cost due to number of excess components required by the individual RPM switches. A more significant shortcoming is the compromise of the overall system integrity that results in the various component intolerances, particularly where two or more separate RPM switches are configured to operate in concert.
While the foregoing tachometer features effectively inform the driver of the proper shift points during "drive time," further assistance is desired. Just as golfer may review a videotape of his golf swing in order to better refine his swing and improve his game, it is known that similar training exercises can help racing drivers improve their driving times.
In this regard, another significant feature found in the prior art is the inclusion of a memory device within a tachometer. These "memory" tachometers are designed to store the engine RPM throughout a racing event, such as a complete drag race, allowing the driver to later review a "replay" of the entire race.
In practice, the engine RPM is sampled at discrete time intervals of sufficiently short duration so that the entire racing event may be accurately recreated for later replay and review by the driver or crewman. From this replay, the driver can identify the particular points at which he shifted, and determine whether he is generally shifting too early or too late. Advantageously, this allows the driver to make adjustments to the timina or technique of his shifting, or engine and suspension set-up etc., that will improve future drive times.
A related feature of these "memory" tachometers is the ability to replay the racing event at a reduced pace, such as one-third the actual recording speed. These tachometers also provide a time counter which displays the elapsed time of the recorded event during memory replay.
While advanced features, such as those described above, allow the driver to observe dynamically the deviations between the targeted or optimum shift points and the actual shift points while the race replay is occurring, further improvements in the art are desired. For example, further improvements are needed that will better enable drivers to more accurately observe the precise RPM and elapsed time at each shift point. Because of the constant movement of the deflection needle and advancing clock display, even when replaying the event at one-third speed the driver still has difficulty in determining the precise RPM and elapsed time at the shifting points.
It is also desired to provide a means for diagnosing possible mechanical or electrical problems within the automobile. It is known, for example, that excessive time required to complete a gear shift may be an indication of clutch slippage. It is also known that if the vehicle requires an excessive amount of time in any particular gear before reaching the targeted shifting RPM, that a particular tuning adjustment may be desired. Accordingly, tachometers are desired that capture and delineate upon replay certain special events that occur during the recorded event.
An additional shortcoming noted in the prior art relates to wasted memory and/or driver distraction, since the driver typically initiates the event recording at some point near the start of the race. Indeed, if the driver signals the tachometer to begin recording too long before the start of the race, then an excessive amount of memory is filled with engine data that is of no use, and possibly to such an extent that too little memory is left to record a complete racing event. Alternatively, if the driver waits too near to the start of the race before signaling the tachometer to begin recording, then it becomes a distraction to the driver when his attention should be focused on the start of the race.
Another shortcoming of the prior art relates to the inability these systems to create a permanent record of the racing event. In the memory tachometer systems, after the driver has recorded a given racing event, he may review or replay that event, but has no means for readily generating a permanent record of the event. To be sure, in some prior art systems the recorded information is lost when the driver resets the device to record a subsequent racing event.